Abu Hamzah says: I asked Ibn Abbas (may Allah be pleased with them both) about "naqd al-witr" (breaking the witr), and he said: When you have prayed witr in the early part of the night, do not pray witr in the last part; and when you have prayed witr at the end of the night, do not pray witr at the beginning. I asked A'idh bin Amr (may Allah be pleased with him), who was one of the Companions of the Prophet (peace and blessings be upon him), about breaking the witr, and he said: When you have prayed witr at the beginning of the night, do not pray it in the last part of the night; and when you have prayed witr in the last part of the night, do not pray it in the early part.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4846